Heretofore, positioning tables of various structures have been devised. For example, a three-layered table is known in which in order to fix a workpiece such as a glass substrate to a predetermined position by moving a workpiece lengthwise, widthwise, and a certain angle about a rotational shaft, there are provided vertically on a base table an X-direction table movable in X-direction, a Y-direction table movable in Y-direction, and .theta.-direction table movable in .theta.-direction. According to this positioning table, the base table is provided with a circular guide and a pulse motor or a servo motor so as to move the .theta.-direction table in .theta.-direction. The .theta.-direction table is provided with a pulse motor or a servo motor through a linear guide and a ball thread so as to move the Y-direction table in Y-direction. The Y-direction table is provided with a pulse motor or a servo motor through a linear guide and a ball thread so as to move the X-direction table in X-direction. Each table is moved along the guide by driving the motor to adjust the positioning of the workpiece in each direction.
However, including the base table, the positioning table of the above construction is four-layered and as such, thick and heavy and in addition, the entire structure thereof is complicated because each table is provided with the guide and the motor except the X-direction table. Accordingly, when a thin film forming apparatus which incorporates the positioning table is used as a moving type table, the apparatus is large-sized. Therefore, the apparatus has an issue that in moving the table or placing the workpiece in position, a prompt operation cannot be carried out.
In order to solve the above issue, the following positioning table has been proposed. According to the positioning table, a driving device such as a pulse motor or a servo motor is provided on one table, three reference pins which are slidably moved by the driving device are arranged to be L-shaped, and a workpiece is pressed by a workpiece pressing device (pusher) to press the workpiece against the reference pins. The positioning of the workpiece in each direction is adjusted by moving each reference pin.
However, in the above construction, when the workpiece is moved in .theta.-direction, the rotational center of the workpiece is not fixed. That is, when each reference pin is moved, the rotational axis of the workpiece is changed. Therefore, when the positioning of the workpiece is carried out based on data, the period of time for locating the workpiece at a predetermined position becomes long.
Accordingly, in order to solve the above-described issue, the object of the present invention is to provide a positioning table which is capable of accomplishing the positioning operation of a workpiece in a short period of time and compact, light, and simple in structure.